JP4551007B2 - Raman amplifier and optical transmission system using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Raman amplifier and an optical transmission system using the Raman amplifier, and more particularly, to a technique for widening a wavelength bandwidth for transmitting signal light.
[0002]
[Prior art]
Conventionally, in a long-distance optical transmission system, 3R processing (timing correction, waveform shaping, signal regeneration) is executed in a state where an optical signal is once converted into an electrical signal in each repeater, and then converted into an optical signal. It was sent to the relay device. However, at present, an optical amplifier that amplifies an optical signal without converting it into an electrical signal has been put into practical use, and a transmission system using the optical amplifier as a linear repeater is being studied. By replacing the repeater with optical / electrical conversion as described above with an optical amplification repeater, the number of parts constituting each repeater is greatly reduced, reliability is improved, and cost reduction is expected. It is.
[0003]
On the other hand, with the spread of the Internet and the like, the amount of information transmitted over a network has increased, and techniques for increasing the capacity of a transmission system have been actively studied. As one of the methods for realizing a large capacity of the transmission system, a wavelength division multiplexing (WDM) optical transmission system has attracted attention. The wavelength division multiplexing optical transmission is a method of multiplexing and transmitting a plurality of signals using a plurality of carrier waves having different wavelengths, and the amount of information that can be transmitted via one optical fiber is dramatically increased.
[0004]
FIG. 29 is a configuration diagram of a general optical repeater transmission system. In this system, wavelength multiplexed light is transmitted from the optical transmitter 100 to the optical receiver 200. In other words, the optical transmitter 100 generates wavelength-multiplexed light by combining signal lights having different wavelengths and sends them to the transmission line. On the other hand, the optical receiver 200 detects each signal by demultiplexing the received wavelength multiplexed light for each wavelength. Here, the transmission path is an optical fiber, and an optical amplifier is provided at predetermined intervals.
[0005]
Each optical amplifier is typically an erbium-doped fiber amplifier (EDFA). Here, a gain wavelength band of a general EDFA is a 1.55 μm band, and that of a GS-EDFA is a 1.58 μm band. Their bandwidth is about 30 nm. Therefore, when an EDFA is provided in the transmission line of the wavelength division multiplexing optical transmission system, the signal light is transmitted using a carrier wave within these gain wavelength bands.
[0006]
In order to increase the capacity of the transmission system, it is effective to increase the number of wavelength multiplexing, and one effective method for increasing the number of wavelength multiplexing is to widen the gain wavelength band. In recent years, a Raman amplifier using Raman scattering has attracted attention as an optical amplification method that can secure a wider gain wavelength band than EDFA.
[0007]
In Raman amplification, gain is obtained on the longer wavelength side than the wavelength of the excitation light by applying the excitation light to the optical fiber. For example, in the case of a GeO2 doped silica (SiO2) optical fiber, a gain is obtained about 100 nm longer than the wavelength of the pumping light in the 1.55 μm band, as shown in FIG. This shift amount is 13.2 terahertz when converted to frequency. Further, the Raman amplifier can amplify an arbitrary wavelength as long as pumping light can be prepared.
[0008]
The Raman amplifier is realized by utilizing the above property. In order to obtain a wide gain wavelength band, a plurality of pump lights having different center frequencies are used as shown in FIG. 30 (b). This method is described in, for example, Y. Emori, et al., “100 nm bandwidth flat gain Raman amplifiers pumped and gain-equalized by 12-wavelength channel WDM high power laser diodes”, OFC'99 PD19 1999. Yes. Thus, a wide gain wavelength band can be secured by using a plurality of pumping lights.
[0009]
FIG. 31 is a configuration diagram of a wavelength division multiplexing optical transmission system using Raman amplification. Excitation light for Raman amplification is basically applied to the transmission line optical fiber so as to be transmitted in the opposite direction to the signal light. At this time, when a plurality of pump lights are used as shown in FIG. 30 (b), pump lights outputted from a plurality of light sources having different oscillation frequencies are given to the transmission line optical fiber by a wavelength synthesizer or the like. .
[0010]
[Problems to be solved by the invention]
As described above, in the Raman amplifier using Raman scattering, a gain in a band having a wavelength of about 100 nm longer than the wavelength of the excitation light is obtained in the 1.55 μm band. For example, in FIG. 32, when the excitation light P1 having the wavelength λ1 is given, a gain is obtained in a wavelength band longer than the wavelength λ1 by about 100 nm (near the wavelength λ3). Similarly, when the pumping light Pk having the wavelength λ2 is given, a gain can be obtained in a band having a wavelength of about 100 nm longer than the wavelength λ2 (in the vicinity of the wavelength λ4). Therefore, if a plurality of pumping lights P1 to Pk are appropriately used, a gain wavelength bandwidth of about 100 nm can be obtained. In this case, the signal lights S1 to SL are transmitted using the gain wavelength band of about 100 nm.
[0011]
However, in the conventional Raman amplifier, the gain wavelength bandwidth is limited by the shift amount between the wavelength of the pumping light and the wavelength of the Raman gain obtained due to the pumping light. That is, when the difference between the wavelength of the pumping light and the wavelength of the Raman gain obtained due to the pumping light is 100 nm, the maximum gain wavelength bandwidth obtained by the Raman amplifier is about 100 nm.
[0012]
An object of the present invention is to provide a Raman amplifier capable of obtaining a wider gain wavelength bandwidth.
[0013]
[Means for Solving the Problems]
A Raman amplifier according to the present invention is configured to amplify a wavelength multiplexed signal light in which a plurality of signal lights are multiplexed by wavelength multiplexing, and includes a first wavelength amplifier for amplifying the wavelength multiplexed signal light and the wavelength multiplexed signal light. A transmission path for propagating pump light, a light source for generating second pump light for amplifying the wavelength multiplexed signal light, and an optical means for supplying the second pump light generated by the light source to the transmission path A Raman amplifier in which at least one of the first pumping light and the second pumping light is disposed within a band of the wavelength multiplexed signal light.
[0014]
In the above configuration, for example, when the first excitation light is appropriately arranged in the band of the wavelength multiplexed signal light and the second excitation light is appropriately arranged on the shorter wavelength side than the wavelength multiplexed signal light, A part of the signal light and the first excitation light are amplified by the two excitation lights, and the other signal light is amplified by the amplified first excitation light. Raman amplification is realized in a band wider than the Raman shift amount.
[0015]
A Raman amplifier according to another aspect of the present invention is configured to amplify a wavelength-multiplexed signal light in which a plurality of signal lights are multiplexed by wavelength multiplexing. A transmission path for propagating auxiliary light having a long wavelength, a light source for generating excitation light for amplifying the wavelength multiplexed signal light, and an optical means for supplying excitation light generated by the light source to the transmission path; Have
[0016]
In the above configuration, the wavelength multiplexed signal light is amplified by the excitation light. The auxiliary light absorbs a part of the energy of the amplified wavelength multiplexed signal light. Therefore, it is avoided that the optical power of the wavelength multiplexed signal light becomes larger than necessary.
[0017]
The optical transmission system of the present invention has a configuration in which a wavelength-multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is amplified by a Raman amplifier, and the Raman amplifier has a frequency of 1 / n of a Raman shift amount. The wavelength multiplexed signal light is amplified using a plurality of excitation lights arranged at intervals (n is an integer).
[0018]
In the above configuration, the pumping light for Raman amplification is arranged at a frequency interval of 1 / n of the Raman shift amount, so that the peak frequency of the Raman gain due to certain pumping light matches the frequency of other pumping light. . Therefore, adjustment of each pumping light power for equalizing the Raman gain is facilitated.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration diagram of an optical transmission system provided with the Raman amplifier of the present invention. This transmission system includes a terminal station 10 and a terminal station 20, and they are connected by a multi-core optical fiber cable. A signal is transmitted bidirectionally between the terminal station 10 and the terminal station 20.
[0020]
The terminal station 10 includes a plurality of optical transmitters 11 and a plurality of optical receivers 12. On the other hand, the terminal station 20 includes a plurality of optical receivers 21 and a plurality of optical transmitters 22. The signal transmitted from each optical transmitter 11 is transmitted via an optical fiber and received by the corresponding optical receiver 21. On the other hand, a signal transmitted from each optical transmitter 22 is transmitted via an optical fiber and received by the corresponding optical receiver 12. Each of the transmitters 11 and 22 transmits wavelength multiplexed light. That is, in this transmission system, wavelength division multiplexed light is transmitted through each optical fiber constituting the multi-core optical fiber cable.
[0021]
A plurality of Raman amplifiers 30-1 to 30-n are provided on the transmission path between the terminal station 10 and the terminal station 20. Each of the Raman amplifiers 30-1 to 30-n amplifies wavelength multiplexed light transmitted through each optical fiber constituting the multi-core optical fiber cable. In Raman amplification, the optical fiber itself functions as an optical amplifier by applying excitation light to the optical fiber. Therefore, the “Raman amplifier” is composed of an optical fiber and a device that supplies the pumping light to the optical fiber, but the device that supplies the pumping light to the optical fiber is sometimes called a “Raman amplifier”. Each Raman amplifier may be provided in the optical repeater.
[0022]
FIG. 2 is a configuration diagram of the Raman amplifier 30. The Raman amplifiers 30-1 to 30-n basically have the same configuration. The “Raman amplifier 30” represents any one of the Raman amplifiers 30-1 to 30-n.
[0023]
The Raman amplifier 30 includes a plurality of excitation light sources 31, a multiplexer 32, and a multiplexer 33. The plurality of excitation light sources 31 generate excitation light having different wavelengths. In this embodiment, excitation light having wavelengths λ1 to λ4 is generated by four excitation light sources. Each excitation light source 31 is, for example, a laser diode. The laser diode generally outputs light having a power corresponding to a given current. Many laser diodes also have a back power monitor function for detecting the light emission power. In the following, it is assumed that the light emission power of each excitation light source 31 can be detected by the back power monitor function or other methods.
[0024]
The multiplexer 32 multiplexes the excitation light output from the plurality of excitation light sources 31. In this embodiment, excitation light of wavelengths λ1 to λ4 is multiplexed by the multiplexer 32. The multiplexer 32 includes a plurality of output ports, and outputs the combined excitation light from each output port. The multiplexer 32 can be realized by a wavelength multiplexing coupler, for example. The multiplexer 33 is provided for each optical fiber accommodated in the multi-core optical fiber cable, and supplies the excitation light output from the multiplexer 32 to the corresponding optical fiber. At this time, the excitation light is basically incident on the optical fiber so as to be transmitted in the opposite direction to the signal light.
[0025]
With the above-described configuration, a plurality of pumping lights having different wavelengths are combined, and the combined pumping lights are respectively supplied to the plurality of optical fibers. In the example shown in FIG. 2, four excitation light sources 31 are provided in the Raman amplifier 30, but the present invention is not limited to this. The number of excitation light sources 31 may be determined based on, for example, a required gain wavelength bandwidth. In this example, the number of pumping light sources 31 and the number of optical fibers match each other. However, the present invention is not limited to this, and these numbers may be different from each other.
[0026]
FIG. 3 is a diagram for explaining the outline of the Raman amplifier of the present embodiment. The Raman amplifier 30 of the present embodiment amplifies wavelength multiplexed light transmitted via a plurality of optical fibers, but the amplification operation for each optical fiber is basically the same as each other. Therefore, hereinafter, the operation of any optical fiber among the plurality of optical fibers accommodated in the multi-core optical fiber cable will be described.
[0027]
In the optical transmission system provided with the Raman amplifier 30, a plurality of signals are multiplexed and transmitted by wavelength multiplexing. That is, a plurality of signals are transmitted using carrier waves having different wavelengths. In this example, it is assumed that these signals are transmitted using carrier waves with wavelengths λ2 to λ4. Hereinafter, a carrier wave for transmitting a signal is referred to as “signal light”. Specifically, in this optical transmission system, signal lights S1 to Sn of wavelengths λ2 to λ4 are multiplexed and transmitted by wavelength multiplexing.
[0028]
The Raman amplifier 30 uses a plurality of excitation lights P1 to Pm. Here, as described with reference to FIG. 2, these pumping lights are generated by the corresponding pumping light sources 31, multiplexed by the multiplexer 32, and supplied to the optical fiber.
[0029]
As shown in FIG. 3, the pumping lights P1 to Pm are arranged in the wavelength bands [lambda] 1 to [lambda] 3. That is, the wavelength band used as excitation light and the wavelength band used as signal light partially overlap each other. Specifically, pumping light PQ + 1 to Pm and signal light S1 to Sr are mixed in the wavelength band λ2 to λ3.
[0030]
As described above, in the optical transmission system in which the Raman amplifier of this embodiment is used, a part of the wavelength band used as the pumping light and a part of the wavelength band used as the signal light overlap each other.
[0031]
In the Raman amplification, as described above, gain is obtained in the wavelength band corresponding to the wavelength of the given excitation light. Here, the difference between the wavelength of the pumping light and the wavelength at which gain is obtained corresponding to the pumping light (hereinafter, the Raman shift amount) is about 100 nm in the 1.55 μm band. For example, if the wavelength of the pumping light is 1.45 μm, the wavelength of the gain peak generated due to the pumping light is about 1.55 μm. Further, if the wavelength of the pumping light is 1.45 + Δμm, the wavelength of the gain peak generated due to the pumping light is about 1.55 + Δμm. That is, the wavelength band of gain obtained in Raman amplification is shifted by about 100 nm from the wavelength band of pumping light. For this reason, in FIG. 3, the wavelength bands λ2 to λ4 for transmitting the signal lights S1 to Sn are shifted by 100 nm with respect to the wavelength bands λ1 to λ3 used as the pumping lights P1 to Pm.
[0032]
FIG. 4 is a diagram for explaining the operation of the Raman amplifier of this embodiment. When pump lights P1 to PQ are given by the Raman amplifier 30, gains are obtained in the wavelength bands λ2 to λ3. Thereby, the signal lights S1 to Sr are amplified by Raman amplification resulting from the excitation lights P1 to PQ. Here, assuming that the difference between the wavelength λ1 and the wavelength λ2 is 100 nm, the gain wavelength bandwidths λ2 to λ3 are also about 100 nm.
[0033]
Similarly, when the pump light PQ + 1 to Pm is given by the Raman amplifier 30, gain is obtained in the wavelength band λ3 to λ4. As a result, the signal lights Sr to Sn are amplified by Raman amplification resulting from the excitation lights PQ + 1 to Pm. Here, since the wavelength bands λ2 to λ3 in which the pumping lights PQ + 1 to Pm are set are 100 nm, the gain bandwidths λ3 to λ4 are also about 100 nm. As a result, the total gain bandwidth λ2 to λ4 is about 200 nm. That is, in the Raman amplifier, a gain wavelength bandwidth larger than the Raman shift amount can be obtained.
[0034]
However, in the system of this embodiment, signal light and excitation light are mixed in the wavelength band λ2 to λ3. Therefore, in this wavelength band, not only the signal light but also the excitation light is amplified by the excitation lights P1 to PQ. Specifically, the signal lights S1 to Sr and the excitation lights PQ + 1 to Pm are amplified by the excitation lights P1 to PQ. As a result, the gains of the wavelength bands λ3 to λ4 depend not only on the pumping lights PQ + 1 to Pm but also on the pumping lights P1 to PQ for amplifying the pumping lights PQ + 1 to Pm. Further, the Raman amplification action is not caused only by continuous wave (CW: continuous wave) such as excitation light, but also caused by discontinuous light such as signal light. Therefore, the signal lights S1 to Sr in the wavelength bands λ2 to λ3 generate gains in the wavelength bands λ3 to λ4. That is, the gains of the wavelength bands λ3 to λ4 also depend on the signal lights S1 to Sr.
[0035]
As described above, when the wavelength band used as the pump light and the wavelength band used as the signal light overlap each other, the adjustment of the gain becomes complicated. A method for adjusting the gain will be described later.
[0036]
FIG. 5 is a diagram for explaining the concept of Raman amplification for obtaining a wider gain wavelength bandwidth. In this example, the excitation lights P1 to Pm are appropriately set in the wavelength band λ1 to λ5. In this case, gains are obtained in the wavelength bands λ2 to λ6 by the pumping lights P1 to Pm. Here, the wavelength bands λ2 to λ6 are shifted from the wavelength bands λ1 to λ5 by about 100 nm. If the difference between the wavelength .lamda.1 and the wavelength .lamda.5 is 300 nm, a gain of about 300 nm can be obtained by the excitation lights P1 to Pm.
[0037]
In the above configuration, gain is obtained in the wavelength bands λ2 to λ6 by the pumping lights P1 to Pm, so that the signal lights S1 to Sn are set in the wavelength bands λ2 to λ6. Therefore, in the wavelength band λ2 to λ5, the excitation light and the signal light are mixed. Specifically, in this wavelength band, pumping lights PQ + 1 to Pm and signal lights S1 to Sr are mixed.
[0038]
FIG. 6 is a diagram for explaining the operation of the Raman amplifier shown in FIG. In this Raman amplifier, three stages of Raman excitation occur. That is, gains are obtained in the wavelength bands λ2 to λ3 by the pumping lights P1 to PQ set in the wavelength bands λ1 to λ2. Further, gains are obtained in the wavelength bands λ3 to λ5 by the pumping lights PQ + 1 to Pk set in the wavelength bands λ2 to λ3. Further, gain is obtained in the wavelength bands λ5 to λ6 by the pumping lights Pk + 1 to Pm set in the wavelength bands λ3 to λ5. Here, if the wavelength bands λ1 to λ2, the wavelength bands λ2 to λ3, and the wavelength bands λ3 to λ5 are each 100 nm, the total gain bandwidth λ2 to λ6 is about 300 nm. That is, according to this Raman amplifier, a gain wavelength bandwidth that is three times the Raman shift amount can be obtained.
[0039]
In the examples shown in FIGS. 3 to 6, a gain wavelength bandwidth that is twice or three times the Raman shift amount is obtained, but the present invention is not limited to this. That is, if a plurality of excitation lights are appropriately set over a wider wavelength band, a wider gain wavelength bandwidth can be obtained. For example, if four stages of Raman excitation occur by appropriately setting a plurality of excitation lights over a wavelength band four times the Raman shift amount, a gain wavelength bandwidth (four times the Raman shift amount) ( That is, 400 nm) is obtained.
[0040]
FIG. 7 is a diagram for explaining a method of arranging signal light and excitation light. The system of the present embodiment is premised on wavelength multiplexing transmission, but the wavelength (frequency) of a carrier to be used in this wavelength multiplexing transmission is defined in ITU-T (International Telecommunication Union Telecommunication standardization sector). And the specification prescribed | regulated in ITU-T is often called the ITU-T grid.
[0041]
The reference frequency of the ITU-T grid is 193.1 THz. As the carrier wave, as shown in FIG. 7 (a), the reference frequency and a frequency obtained by shifting the reference frequency by 25 GHz are used. In this band, 25 GHz corresponds to about 0.2 nm.
[0042]
The plurality of signal lights are basically set according to the ITU-T grid. Specifically, the plurality of signal lights are set every 25 GHz (about every 0.2 nm). A plurality of excitation lights are also set according to the ITU-T grid. That is, the frequency of each pumping light is basically 193.1 ± 0.025 × n (THz). Here, “n” is an integer. However, the excitation light is set at an interval larger than the interval at which the signal light is set.
[0043]
Thus, in this embodiment, both the signal light and the excitation light are set according to the ITU-T grid. At this time, the signal light is basically set every 25 GHz, but is not set to the wavelength at which the excitation light should be set. That is, the same wavelength is not assigned to the signal light and the excitation light. Further, since the power of the pumping light is usually larger than the power of the signal light, the spectrum of the pumping light is wider than that of the signal light as shown in FIG. 7 (b). For this reason, when assigning a certain wavelength to the excitation light, several wavelengths close to the wavelength are not assigned to the signal light.
[0044]
The plurality of excitation lights are basically arranged at regular intervals as shown in FIG. When a plurality of pump lights are arranged at equal intervals, it is relatively easy to adjust the Raman gain by controlling the power of the pump lights.
[0045]
Next, several configurations and methods for supplying excitation light to the transmission line will be described. In the following, it is assumed that the signal lights S1 to Sn are amplified by the excitation lights P1 to Pm.
[0046]
FIG. 9 is a diagram illustrating an example of a method for supplying excitation light to a transmission line. In this method, pumping lights P 1 to PQ are supplied from each Raman amplifier 30, and pumping lights PQ + 1 to Pm are supplied from the terminal station 10.
[0047]
The terminal station 10 includes a signal light source 41 for generating the signal lights S1 to Sn, an excitation light source 42 for generating the excitation lights PQ + 1 to Pm, and multiplexing for combining these signal lights and excitation lights. A container 43 is provided. As a result, the signal light and the excitation light are multiplexed by wavelength multiplexing and sent to the transmission line optical fiber. Note that the wavelengths of the signal lights S1 to Sn and the excitation lights PQ + 1 to Pm are longer than the wavelength [lambda] 2 shown in FIGS.
[0048]
Each Raman amplifier 30 includes a pumping light source 31 for generating pumping lights P1 to PQ and a multiplexer 33 for guiding the pumping light to the transmission path. Here, the excitation light source 31 is, for example, a plurality of laser diodes LD for generating these excitation lights. Further, these excitation lights are combined by a multiplexer (multiplexer 32 in FIG. 2) and supplied to a multiplexer 33. Note that the wavelengths of the excitation lights P1 to PQ are shorter than the wavelength [lambda] 2 shown in FIGS.
[0049]
The multiplexer 33 includes three input / output ports (ac ports). The a port is connected to the optical fiber on the terminal station 10 side, the b port is connected to the optical fiber on the terminal station 20 side, and the c port receives the pumping light generated by the pumping light source 31. When the light having a wavelength longer than the wavelength .lambda.2 is received from the a port, the multiplexer 33 outputs it through the b port. That is, when the multiplexer 33 receives the signal lights S1 to Sn and the pumping lights PQ + 1 to Pm via the optical fiber on the terminal station 10, the multiplexer 33 outputs them via the optical fiber on the terminal station 20 side. Further, the multiplexer 33, when receiving light having a wavelength shorter than the wavelength λ2 from the c port, outputs it through the a port. That is, the multiplexer 33 guides the pumping lights P1 to PQ received through the c port to the optical fiber on the terminal station 10 side.
[0050]
Next, the operation of the Raman amplifier configured as described above will be described with reference to FIG. In the above configuration, the pumping lights P1 to PQ generated by the pumping light source 31 are supplied to the transmission line optical fiber. As a result, gain is obtained in the wavelength band λ2 to λ3. That is, the lights arranged in the wavelength bands λ2 to λ3 are amplified by the excitation lights P1 to PQ. Specifically, the signal lights S1 to Sr and the excitation lights PQ + 1 to Pm arranged in the wavelength bands λ2 to λ3 are amplified. Further, gains are obtained in the wavelength bands λ3 to λ4 by the amplified pumping lights PQ + 1 to Pm. That is, the signal lights Sr + 1 to Sn arranged in the wavelength bands λ3 to λ4 are amplified by the pumping lights PQ + 1 to Pm. In this way, the signal lights S1 to Sn are amplified by each Raman amplifier 30.
[0051]
FIG. 10 is a diagram illustrating another example of a method for supplying excitation light to a transmission line. In this method, pumping lights P1 to Pm are supplied by each Raman amplifier 30.
The terminal station 10 includes a signal light source 41 for generating signal lights S1 to Sn. These signal lights S1 to Sn are multiplexed by wavelength multiplexing and sent to the transmission line optical fiber.
[0052]
Each Raman amplifier 30 includes a pumping light source 31 for generating pumping lights P1 to Pm and an optical circulator 34 that guides the pumping light to a transmission path. Here, the excitation light source 31 is, for example, a plurality of laser diodes LD for generating these excitation lights. Further, these excitation lights are multiplexed by a multiplexer (not shown) (multiplexer 32 in FIG. 2) and supplied to the optical circulator 34.
[0053]
The optical circulator 34 includes three input / output ports (ac ports). Here, the light input from the a port is guided to the b port, the light input from the b port is guided to the c port, and the light input from the c port is guided to the a port. Therefore, the optical circulator 34 guides the signal lights S1 to Sn input through the optical fiber on the terminal station 10 side to the optical fiber on the terminal station 20 side. The optical circulator 34 guides the pumping lights P1 to Pm generated by the pumping light source 31 to the optical fiber on the terminal station 10 side.
[0054]
Next, the operation of the Raman amplifier configured as described above will be described with reference to FIG. In the above configuration, the pumping lights P1 to Pm generated by the pumping light source 31 are supplied to the transmission line optical fiber. As a result, gain is obtained in the wavelength band λ2 to λ4. That is, the signal lights S1 to Sn arranged in the wavelength bands λ2 to λ4 are amplified by the pumping lights P1 to Pm.
[0055]
FIG. 11 is a modification of the method shown in FIG. In this method, pumping lights P1 to Pm are supplied by each Raman amplifier 30, and the terminal station 10 supplies pumping lights (pumping lights PQ + 1 to Pm) within a wavelength band in which signal light is arranged. . The operation of this configuration is basically the same as the operation described with reference to FIG.
[0056]
In the systems shown in FIGS. 9 to 11, it is basically desirable that the optical spectrum width of each excitation light be narrow. It is desirable that at least the spectrum width of the excitation light (for example, excitation light PQ + 1 to Pm) arranged in the band where the signal light is arranged is about the same as that of the signal light. The optical spectrum width of each excitation light is adjusted by, for example, an optical fiber grating.
[0057]
By the way, in the wavelength division multiplexing transmission system, it is generally desirable that the level of each signal light included in the wavelength division multiplexed light is equalized. In order to equalize the level of each signal light included in the wavelength multiplexed light, it is necessary to adjust the gain of each amplifier. Hereinafter, a method for adjusting the gain of each Raman amplifier will be described.
[0058]
FIG. 12 is a diagram for explaining the function of adjusting the gain in each Raman amplifier 30. The Raman amplifier 30 includes a plurality of excitation light sources 51. These excitation light sources 51 are laser diodes having different oscillation frequencies, and are driven by corresponding drive circuits 52. The drive circuit 52 supplies a current to the corresponding excitation light source 51 in accordance with an instruction from the control unit 54. Furthermore, each of the detection circuits 53 detects the gain of the corresponding wavelength within the wavelength band in which the signal light is transmitted. A known technique is used as a method for detecting the gain for each wavelength.
[0059]
The control unit 54 checks the gain for each wavelength in accordance with the inquiry from the terminal station 10 or 20. At this time, the output of each detection circuit 53 is referred to. Then, the control unit 54 notifies the terminal station 10 or 20 of the detection result. Further, the control unit 54 controls the drive circuit 62 in accordance with an instruction from the terminal station 10 or 20. Thereby, based on the instruction | indication from the terminal station 10 or 20, the light emission power of the specific excitation light source 51 is adjusted.
[0060]
The terminal station 10 or 20 includes a control circuit for adjusting the gain of each Raman amplifier. This control circuit adjusts the gain of each Raman amplifier at the time of construction of this optical transmission system or periodically thereafter. Specifically, this control circuit first inquires each Raman amplifier about the gain for each wavelength. Then, according to the response to the inquiry, an instruction is given so that the wavelength characteristic of the gain in each Raman amplifier is equalized. For example, when a gain at a certain wavelength is relatively low in a certain Raman amplifier, an instruction to increase the power of pumping light having a wavelength shorter by about 100 nm than that wavelength is sent to the Raman amplifier. . In this case, the Raman amplifier that has received the instruction adjusts the power of the corresponding excitation light in accordance with the instruction. Thereby, the gain in each Raman amplifier is equalized.
[0061]
In the case where a part of the pumping light (pumping light PQ + 1 to Pm) is generated by the terminal station 10 as in the configuration shown in FIG. 9, only the pumping light generated by each Raman amplifier is adjusted. In addition, it is necessary to adjust the excitation light generated by the terminal station 10. In this case, if the terminal station 10 manages the gain of each Raman amplifier, the terminal station 10 itself may adjust the pumping lights PQ + 1 to Pm. If the terminal station 20 manages the gain of each Raman amplifier, the pumping lights PQ + 1 to Pm may be adjusted based on the notification from the terminal station 20 to the terminal station 10.
[0062]
As described above, in the system of this embodiment, the wavelength deviation of the gain in each Raman amplifier is reduced by appropriately adjusting the optical powers of the pumping lights P1 to Pm.
[0063]
FIG. 13 is a diagram for explaining a method of adjusting the optical S / N ratio of the signal lights S1 to Sn. The optical S / N ratio of the signal lights S1 to Sn is basically controlled by adjusting the optical power of the signal lights S1 to Sn generated by the signal light source 41. For this reason, in the system of the present embodiment, the optical S / N ratio is detected for each wavelength in the receiving-side terminal station (terminal station 20), and the detection result is fed back to the transmitting-side terminal station (terminal station 10). The
[0064]
The terminal station 20 includes a branch coupler 61 for branching the wavelength multiplexed light including the signal lights S1 to Sn, a demultiplexer 62 for extracting the signal lights S1 to Sn from the wavelength multiplexed light branched by the branch coupler 61, and a splitter. An S / N detection circuit 63 for detecting an optical S / N ratio for each of the signal lights S1 to Sn taken out by the waver 62 is provided. Further, the control circuit 64 examines the deviation of the optical S / N ratio of the signal lights S1 to Sn based on the output of each S / N detection circuit 63 and creates an instruction for reducing the deviation. Specifically, for example, if the optical S / N ratio of signal light of a certain wavelength is relatively poor, an instruction to increase the power of signal light of that wavelength is created. Then, the created instruction is sent to the terminal station 10.
[0065]
When receiving the instruction from the terminal station 20, the terminal station 10 adjusts the power of the signal light source 41 accordingly. Thereby, the deviation of the light S / N ratio of the signal lights S1 to Sn is reduced.
[0066]
Thus, in the optical transmission system of this embodiment, the gain by Raman amplification and the optical S / N ratio of signal light are individually adjusted. That is, the optical power of each pumping light is appropriately adjusted (pumping light pre-emphasis) to reduce the deviation of the Raman gain depending on the wavelength, and the deviation of the optical S / N ratio of the plurality of signal lights is reduced. Therefore, the optical power of each signal light is appropriately adjusted (signal light pre-emphasis).
[0067]
As described above, in the Raman amplifier of this embodiment, a part of the signal light (for example, S1 to Sr in FIG. 3) works as excitation light for the signal light on the longer wavelength side. However, since the optical power of each signal light is sufficiently smaller than that of the pump light, the gain generated by the signal light is smaller than the gain generated by the pump light. Therefore, the gain of the Raman amplifier is generally adjusted to a desired characteristic by controlling the optical power of each pumping light. At this time, the optical power of the signal light may be finely adjusted as necessary. Further, instead of the S / N detection circuit, it is also possible to use the code error rate of the optical receiver for each wavelength.
[0068]
Next, a method for improving the transmission performance of the optical transmission system using the characteristics of Raman amplification will be described.
FIG. 14 is a configuration diagram of an optical transmission system provided with a mixed transmission line fiber. In this system, a mixed transmission line fiber is used as an optical fiber for transmitting wavelength division multiplexed light. The mixed transmission line fiber includes a first optical fiber and a second optical fiber having a smaller mode field diameter (effective cross-sectional area or core diameter) than that of the first optical fiber. Here, as one embodiment, it is desirable that the first optical fiber has positive dispersion and the second optical fiber has negative dispersion. Then, when the signal light is transmitted from the optical transmitter 11 to the optical receiver 21, the signal light is first propagated through the first optical fiber on each mixed transmission path, and then through the second optical fiber. Propagated.
[0069]
FIG. 15 is a configuration diagram of a Raman amplifier in the system shown in FIG. Here, any one of a plurality of Raman amplifiers provided on the transmission line is shown.
[0070]
The Raman amplifier 30 supplies the excitation light to the transmission line so that the excitation light is transmitted in the direction opposite to the signal light. That is, the excitation light is supplied to the transmission line by the backward excitation method. For this reason, the excitation light generated by the excitation light source 31 is first supplied to the second optical fiber, and then supplied to the first optical fiber after passing through the second optical fiber. Here, in Raman amplification, as is well known, the higher the power density of the pumping light supplied to the optical fiber, the more efficient gain is obtained. That is, in the Raman amplification, the gain can be obtained more efficiently as the mode field diameter of the optical fiber is smaller. Therefore, in the configuration of the present embodiment, a gain can be obtained efficiently in the second optical fiber. As a result, the optical S / N ratio of the signal light is improved.
[0071]
Further, in this system, nonlinear effects on the optical transmission line can be suppressed. Here, as is well known, the nonlinear effect on the optical transmission line increases as the mode field diameter of the optical fiber decreases, and increases as the optical power of the signal light increases. However, in this system, when the optical power of the signal light is large, the nonlinear effect is small because the light is propagated through the first optical fiber having a relatively large mode field diameter. Further, since the signal light is sufficiently attenuated when it reaches the second optical fiber having a small mode field diameter, the nonlinear effect generated in the second optical fiber is also small. That is, nonlinear effects are suppressed in all transmission paths, and transmission waveform distortion is reduced.
[0072]
As described above, when the mixed transmission path composed of the first and second optical fibers is used, the optical S / N ratio of the signal light is improved and the distortion of the signal waveform due to the nonlinear effect is suppressed. The ratio of the length of the first optical fiber to the length of the second optical fiber is, for example, 2: 1. The effective areas of the first and second optical fibers are, for example, about 110 micrometer square and 20 micrometer square, respectively.
[0073]
In the examples shown in FIGS. 14 and 15, the mixed transmission line fiber is composed of two types of optical fibers having different mode field diameters, but the present invention is not limited to this. That is, the mixed transmission line fiber may be composed of three or more types of optical fibers. For example, in the example shown in FIGS. 16 and 17, each mixed transmission line fiber is composed of first to third optical fibers. In this case, the mode field diameter of the first optical fiber is the largest, and the mode field diameter of the third optical fiber is the smallest. As described above, the mixed transmission line fiber may be configured by connecting a plurality of types of optical fibers so that the mode field diameter gradually decreases in the direction in which the signal light is transmitted.
[0074]
By the way, in Raman amplification, as described with reference to FIGS. 3 to 6, when pump light is supplied to an optical fiber, gain is increased in a wavelength band shifted from the wavelength of the pump light to the longer wavelength side by the amount of Raman shift. can get. At this time, if light exists in the gain wavelength band, the light is amplified. For example, in FIG. 4, when pumping light P1 to PQ is supplied to the optical fiber, light (including signal light and pumping light) arranged in the wavelength band λ2 to λ3 is amplified. At this time, the light arranged in the wavelength band λ2 to λ3 is amplified by absorbing a part of the energy given as the excitation light P1 to PQ.
[0075]
As described above, the Raman amplification occurs when the energy given as the excitation light is absorbed by the light arranged on the longer wavelength side than the wavelength of the excitation light. At this time, when a part of the energy of the pumping light is absorbed by the other light, the optical power of the pumping light decreases accordingly. On the other hand, the optical power of the excitation light hardly decreases unless a part of the energy is absorbed by other light. That is, the optical power of the excitation light may vary depending on whether a part of the energy is absorbed by other light.
[0076]
This problem is not limited to the excitation light. For example, in FIG. 4, the energy of the light arranged in the wavelength band λ1 to λ2 is absorbed by the light arranged in the wavelength band λ2 to λ3, and the energy of the light arranged in the wavelength band λ2 to λ3 is the wavelength. It is absorbed by the light arranged in the bands λ3 to λ4. However, the energy of light arranged in the wavelength band λ3 to λ4 is not absorbed by other light. As a result, the gain in the wavelength band λ3 to λ4 may become larger than necessary. Alternatively, the level of the signal light arranged in the wavelength band λ3 to λ4 may become higher than necessary.
[0077]
In the system of this embodiment, in order to solve the above-described problem, as shown in FIG. 18, auxiliary lights A1 to At are arranged on the longer wavelength side than the wavelength band in which the signal lights S1 to Sn are arranged. As a result, the energy of the signal lights Sr to Sn arranged in the wavelength bands λ3 to λ4 is absorbed by the auxiliary lights A1 to At. That is, the gain in the wavelength band λ3 to λ4 is appropriately suppressed.
[0078]
The auxiliary lights A1 to At can also be used in a system in which three or more stages of Raman amplification are performed. FIG. 19 shows an example in which auxiliary lights A1 to At are arranged in a system in which three-stage Raman amplification is performed.
[0079]
The auxiliary lights A1 to At may be generated by the terminal station 10 or may be generated by each Raman amplifier 30. Examples of the configuration of a system provided with an auxiliary light source for generating auxiliary lights A1 to At are shown in FIGS. In the example shown in FIGS. 20 and 22, the auxiliary light source 71 for generating the auxiliary lights A1 to At is provided in each Raman amplifier 30. In this case, the auxiliary lights A1 to At are supplied to the transmission line optical fiber together with the pumping lights P1 to Pm. On the other hand, in the example shown in FIGS. 21 and 23, the auxiliary light source 71 for generating the auxiliary lights A1 to At is provided in the terminal station 10. In this case, the auxiliary lights A1 to At are multiplexed with the signal lights S1 to Sn by wavelength multiplexing and propagated through the transmission line.
[0080]
The auxiliary lights A1 to At may be arranged according to the ITU-T grid shown in FIG. 7A, similarly to the signal light or the excitation light. In addition, the auxiliary lights A1 to At may be arranged at a constant frequency interval, like the excitation light.
[0081]
Further, the auxiliary lights A1 to At may be used as a carrier wave for transmitting a monitoring signal for the terminal station 10 or 20 to check the state of each Raman amplifier or transmission line. However, in this case, the auxiliary lights A1 to At basically need to be generated by the terminal station. The monitoring signal may be transmitted using the excitation lights P1 to Pm.
[0082]
Further, the optical power of the auxiliary lights A1 to At may be adjusted according to an instruction from the terminal station 10 or 20. In this case, the optical powers of the auxiliary lights A1 to At are adjusted so that the gain of the wavelength band in which the signal light is arranged is equalized. Specifically, for example, the optical power of the auxiliary lights A1 to At is adjusted based on whether or not the gain in the long wavelength region in the wavelength band in which the signal light is arranged is relatively high. .
[0083]
FIG. 24 is a block diagram of the optical transmission system of the present invention. In this system, a plurality of Raman amplifiers 30 are provided on a transmission line, and an amplifier using a rare earth-doped fiber (hereinafter referred to as a rare earth-doped fiber amplifier) is provided at a terminal station. In this system, signal light is transmitted using a wavelength band of 100 nm or more by using the above-described Raman amplifier. Although not illustrated in FIG. 24, the rare earth doped fiber amplifier is also provided in the terminal station 10.
[0084]
As is well known, the gain wavelength band of a rare earth-doped fiber amplifier varies depending on the material injected into the optical fiber. However, the effective gain wavelength band width of the rare earth doped fiber amplifier is usually about 30 to 40 nm. Therefore, in order to amplify wavelength multiplexed signal light having a wavelength band of 100 nm or more, it is necessary to use a plurality of rare earth doped fiber amplifiers having different gain wavelength bands. In the example shown in FIG. 24, rare earth doped fiber amplifiers 81a to 81n having different gain wavelength bands are provided at the terminal stations. The wavelength-division multiplexed signal light is demultiplexed for each gain wavelength band of the rare-earth doped fiber amplifiers 81a to 81n by a demultiplexer (not shown) at the terminal station 20, and amplified by the corresponding rare-earth doped fiber amplifiers 81a to 81n. . In the following, a method for effectively arranging pumping light for Raman amplification in an optical transmission system in which a Raman amplifier and a rare earth doped fiber amplifier are mixed will be described.
In the system of the present embodiment, the plurality of excitation lights are arranged so as to satisfy the following expression (1). Here, “Δfr” is a Raman shift amount, “Δfe” is an interval at which the excitation light is to be arranged, and “n” is an arbitrary integer.
[0085]
Δfr = n · Δfe (1)
FIG. 25A is a correspondence table showing gain bandwidths when “n = 1 to 6” is substituted into the above equation (1). The Raman shift amount (Δfr) is 13.2 THz. In this case, when 1 to 6 is given as “n”, 13.2 to 2.2 THz is obtained as the interval (Δfe) where the excitation light should be arranged. These intervals are 105.7 to 17.6 nm, respectively, when converted to wavelengths in the vicinity of 1550 nm. Here, the gain bandwidth of the rare earth doped fiber amplifier is 30 to 40 nm, respectively. Therefore, in order to reduce the number of rare earth doped fiber amplifiers 81a to 81n as much as possible, “3” is preferable as “n” to be given to the above equation (1).
[0086]
FIG. 26 shows an embodiment in which excitation light is arranged based on the above equation (1). Here, the case where “n = 3” is given in the above equation (1) is shown. That is, the excitation lights P1 to P10 are arranged every 4.4 THz.
[0087]
The wavelength band in which the signal light is arranged is 1435 to 1667 nm in this embodiment. Then, this signal light wavelength band is collectively amplified by each Raman amplifier 30 by using the pumping lights P1 to P10 on the transmission line. On the other hand, in the terminal station, this signal light wavelength band is amplified for each wavelength band by a plurality of rare earth doped fiber amplifiers 81a to 81n. Specifically, this signal light wavelength band is demultiplexed into seven wavelength bands (S ++ band, S + band, S band, C band, L band, L + band, L ++ band), respectively. Amplified by corresponding rare earth doped fiber amplifiers 81a-81n. Here, the S ++ band to the L ++ band refer to wavelength bands (or frequency bands) partitioned by the excitation lights P4 to P10 in this embodiment. That is, the width of the S ++ band to the L ++ band is 4.4 (about 30 to 40 nm), respectively. Therefore, the rare earth doped fiber amplifiers 81a to 81n can amplify the corresponding S ++ band to L ++ band, respectively. Specifically, for example, the rare earth doped fiber amplifier 81a amplifies the wavelength band 1435 to 1467 nm, and the rare earth doped fiber amplifier 81b amplifies the wavelength band 1467 to 1500 nm.
[0088]
Further, according to the above equation (1), each pump light is arranged so that the peak wavelength of the Raman gain due to each pump light matches the wavelength of the corresponding pump light. For example, the wavelength at which the Raman gain due to the pumping light P1 reaches the peak coincides with the wavelength of the pumping light P4, and the wavelength at which the Raman gain due to the pumping light P2 reaches the peak coincides with the wavelength of the pumping light P5. Therefore, it is expected that the work (pre-emphasis) of adjusting the optical power of each pumping light to equalize the Raman gain is facilitated.
[0089]
In the system of another form of the present embodiment, the plurality of excitation lights are arranged so as to satisfy the following expression (2). Here, “Δfr” is a Raman shift amount, “Δfe” is an interval at which the excitation light is to be arranged, and “n” is an arbitrary integer.
[0090]
Δfr = (n + 0.5) · Δfe (2)
FIG. 25B is a correspondence table showing gain bandwidths when “n = 1 to 6” is substituted into the above equation (2). As shown in FIG. 25 (b), when 1 to 6 are given as “n”, 8.8 to 2.0 THz are obtained as the intervals (Δfe) where the excitation light should be arranged, respectively. These intervals are 70.5 to 16.3 nm when converted to wavelengths in the vicinity of 1550 nm. Here, considering that the gain bandwidth of the rare earth doped fiber amplifier is 30 to 40 nm, “2” or “3” is preferable as “n” to be given to the above equation (2).
[0091]
FIG. 27 shows an embodiment in the case where the excitation light is arranged based on the above (2). Here, the case where “n = 3” is given in the above equation (2) is shown. That is, the excitation lights P1 to P10 are arranged every 3.77 THz. Also in this embodiment, the signal light wavelength band is demultiplexed into a plurality of wavelength bands (S ++ band to L ++ band) as in the method shown in FIG. Amplified by 81a-81n.
[0092]
According to the above equation (2), the peak wavelength of Raman gain due to each pumping light is approximately halfway between the wavelengths of the nth pumping light and the (n + 1) th pumping light when viewed from the pumping light. It becomes. For example, the wavelength at which the Raman gain due to the pumping light P1 reaches a peak is approximately halfway between the wavelengths of the pumping light P4 and the pumping light P5. In this embodiment, the wavelength bands (S ++ band to L ++ band) partitioned by the pumping lights P4 to P10 are amplified by the corresponding rare earth doped fiber amplifiers 81a to 81n. Therefore, the peak frequency of the Raman gain due to each pumping light is approximately the center of the gain wavelength band of the corresponding rare earth-doped fiber amplifier 81a to 81n.
Therefore, a stable amplification operation is expected.
[0093]
Finally, a method for arranging supervisory control light for transmitting supervisory signals for the terminal station 10 or 20 to check the state of each Raman amplifier or transmission line will be described.
The supervisory control light is a carrier wave that transmits a supervisory signal for monitoring the transmission system. The transmission speed of the monitoring signal is sufficiently low compared with the signal transmitted by the signal light. For example, the transmission speed of a signal transmitted by signal light is about 10 Gbps, while that of a monitoring signal is about several tens of kbps to several Mbps. Therefore, the supervisory control light can be received even if its optical S / N ratio is smaller than that of the signal light.
[0094]
By the way, the optical power of the excitation light is sufficiently larger than that of the signal light. For this reason, the optical spectrum width of the excitation light is quite wide, and disturbances (crosstalk, four-wave mixing, etc.) are large in the vicinity of the excitation light. That is, the optical S / N ratio is expected to deteriorate in the vicinity of the excitation light. For this reason, in the system according to the present embodiment, as shown in FIG. 28, monitoring control light having resistance to the optical S / N ratio is arranged in the vicinity of the excitation light. Thereby, the wavelength band far from the excitation light is not used by the monitoring control light, and the signal light can be arranged efficiently.
[0095]
(Appendix 1) A Raman amplifier that amplifies wavelength multiplexed signal light in which a plurality of signal lights are multiplexed by wavelength multiplexing,
A transmission path for propagating the wavelength-division multiplexed signal light and the first pumping light for amplifying the wavelength-multiplexed signal light;
A light source that generates second excitation light for amplifying the wavelength-multiplexed signal light;
Optical means for supplying the second excitation light generated by the light source to the transmission path,
A Raman amplifier in which at least one of the first pumping light and the second pumping light is disposed in a band of the wavelength multiplexed signal light.
(Appendix 2) A Raman amplifier that amplifies wavelength multiplexed signal light in which a plurality of signal lights are multiplexed by wavelength multiplexing,
A transmission path for propagating the wavelength multiplexed signal light;
A light source that generates first excitation light disposed within the band of the wavelength multiplexed signal light and second excitation light disposed outside the band of the wavelength multiplexed signal light;
Optical means for supplying the first excitation light and the second excitation light generated by the light source to the transmission path;
Having a Raman amplifier.
(Appendix 3) The Raman amplifier according to Appendix 1 or Appendix 2,
The wavelength of the second excitation light is shorter than the wavelength of the wavelength multiplexed signal light.
(Appendix 4) The Raman amplifier according to appendix 1 or appendix 2,
The first excitation light and the second excitation light are arranged at equal frequency intervals.
(Appendix 5) The Raman amplifier according to Appendix 1 or Appendix 2,
The first excitation light is arranged according to an ITU-T grid.
(Appendix 6) The Raman amplifier according to appendix 1 or appendix 2,
Each of the first excitation light and the second excitation light is composed of two or more waves.
(Appendix 7) The Raman amplifier according to Appendix 1 or Appendix 2,
The first excitation light is amplified by the second excitation light.
(Appendix 8) A Raman amplifier that amplifies wavelength multiplexed signal light in which a plurality of signal lights are multiplexed by wavelength multiplexing,
A transmission path for propagating the wavelength multiplexed signal light and the first pumping light;
A light source that generates second excitation light disposed within the band of the wavelength multiplexed signal light and third excitation light disposed outside the band of the wavelength multiplexed signal light;
Optical means for supplying the second excitation light and the third excitation light generated by the light source to the transmission path;
Having a Raman amplifier.
(Supplementary Note 9) A Raman amplifier is provided between the first terminal device and the second terminal device, and wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is the first terminal station. An optical transmission system transmitted from a device to the second terminal device,
The first terminal device is
A signal light source for generating the wavelength-multiplexed signal light;
A first excitation light source for generating first excitation light,
The Raman amplifier is
A transmission path for propagating the wavelength multiplexed signal light and the first pumping light;
A second excitation light source for generating second excitation light;
Optical means for supplying the second excitation light generated by the second excitation light source to the transmission path,
At least a part of the first pumping light is arranged in a band of the wavelength multiplexed signal light,
An optical transmission system in which the optical powers of the first and second pump lights are adjusted so that gains by the Raman amplifier are equalized.
(Supplementary Note 10) A Raman amplifier is provided between the first terminal device and the second terminal device, and wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is the first terminal station. An optical transmission system transmitted from a device to the second terminal device,
The first terminal device is
A signal light source for generating the wavelength-multiplexed signal light,
The Raman amplifier is
A transmission path for propagating the wavelength multiplexed signal light;
A first pumping light source for generating first pumping light arranged in the band of the wavelength multiplexed signal light;
A second pumping light source for generating a second pumping light disposed outside the band of the wavelength multiplexed signal light;
Optical means for supplying the first excitation light generated by the first excitation light source and the second excitation light generated by the second excitation light source to the transmission line,
An optical transmission system in which the optical powers of the first and second pump lights are adjusted so that gains by the Raman amplifier are equalized.
(Appendix 11) The optical transmission system according to Appendix 9 or Appendix 10,
The optical powers of the first and second excitation lights are adjusted according to instructions from the first or second terminal device.
(Supplementary note 12) The optical transmission system according to supplementary note 9 or supplementary note 10,
The power of the signal light is adjusted based on the optical S / N ratio of each signal light detected by the second terminal device.
(Additional remark 13) It is the optical amplification method which amplifies the wavelength multiplexing signal light by which the several signal light was multiplexed by wavelength multiplexing using a Raman amplifier,
An optical amplification method for supplying pump light having a wavelength shorter than the wavelength of the wavelength-multiplexed signal light and pump light in a band in which the wavelength-multiplexed signal light is disposed to the transmission path through which the wavelength-multiplexed signal light is propagated.
(Supplementary note 14) A Raman amplifier that amplifies wavelength multiplexed signal light in which a plurality of signal lights are multiplexed by wavelength multiplexing,
A transmission path for propagating auxiliary light having a wavelength longer than the wavelength-multiplexed signal light and the wavelength-multiplexed signal light;
A light source that generates excitation light for amplifying the wavelength-multiplexed signal light;
Optical means for supplying excitation light generated by the light source to the transmission path;
Having a Raman amplifier.
(Supplementary note 15) A Raman amplifier that amplifies wavelength multiplexed signal light in which a plurality of signal lights are multiplexed by wavelength multiplexing,
A transmission path for propagating the wavelength multiplexed signal light;
A light source for generating auxiliary light having a wavelength longer than the wavelength of the wavelength multiplexed signal light and the excitation light for amplifying the wavelength multiplexed signal light;
Optical means for supplying excitation light and auxiliary light generated by the light source to the transmission line;
Having a Raman amplifier.
(Supplementary note 16) The Raman amplifier according to supplementary note 14 or supplementary note 15,
The auxiliary lights are arranged at equal frequency intervals.
(Supplementary note 17) The Raman amplifier according to supplementary note 14 or supplementary note 15,
The auxiliary light is arranged according to an ITU-T grid.
(Supplementary note 18) The Raman amplifier according to supplementary note 14 or supplementary note 15,
The auxiliary light is composed of two or more waves.
(Supplementary note 19) The Raman amplifier according to supplementary note 14 or supplementary note 15,
The auxiliary light is disposed so as to absorb energy of a part of the plurality of signal lights.
(Supplementary note 20) A Raman amplifier is provided between the first terminal device and the second terminal device, and the wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is the first terminal station. An optical transmission system transmitted from a device to the second terminal device,
The first terminal device is
A signal light source for generating the wavelength-multiplexed signal light;
An auxiliary light source for generating auxiliary light having a wavelength longer than the wavelength of the wavelength multiplexed signal light,
The Raman amplifier is
A transmission path for propagating the wavelength multiplexed signal light and auxiliary light;
An excitation light source for generating excitation light for amplifying the wavelength multiplexed signal light;
Optical means for supplying excitation light generated by the excitation light source to the transmission path,
An optical transmission system in which the optical power of the auxiliary light is adjusted so that the gain by the Raman amplifier is equalized.
(Supplementary Note 21) A Raman amplifier is provided between the first terminal device and the second terminal device, and wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is the first terminal station. An optical transmission system transmitted from a device to the second terminal device,
The first terminal device is
A signal light source for generating the plurality of signal lights,
The Raman amplifier is
A transmission path for propagating the wavelength multiplexed signal light;
An excitation light source for generating excitation light for amplifying the wavelength multiplexed signal light;
An auxiliary light source for generating auxiliary light having a wavelength longer than the wavelength of the wavelength multiplexed signal light;
Optical means for supplying excitation light generated by the excitation light source and auxiliary light generated by the auxiliary light source to the transmission path;
An optical transmission system in which the optical power of the auxiliary light is adjusted so that the gain by the Raman amplifier is equalized.
(Appendix 22) The optical transmission system according to Appendix 20 or Appendix 21,
The optical power of the auxiliary light is adjusted according to an instruction from the first or second terminal device.
(Supplementary note 23) The optical transmission system according to supplementary note 20 or supplementary note 21,
A monitoring signal for monitoring the state of the transmission system is carried by the auxiliary light.
(Supplementary Note 24) An optical transmission system in which a wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is amplified by a Raman amplifier, wherein the Raman amplifier has a frequency interval of 1 / n of a Raman shift amount. An optical transmission system (n is an integer) that amplifies the wavelength-division multiplexed signal light using a plurality of pumping lights arranged in (1).
(Supplementary Note 25) An optical transmission system in which a wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is amplified by a Raman amplifier and a rare earth doped fiber amplifier,
The Raman amplifier amplifies the wavelength-multiplexed signal light using a plurality of pump lights arranged at a frequency interval of 1 / n of a Raman shift amount,
The rare earth-doped fiber amplifier is composed of a plurality of amplification units corresponding to the plurality of pump lights, and each amplification unit amplifies signal light in a corresponding wavelength band (n is an integer).
(Supplementary note 26) An optical transmission system in which a wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is amplified by a Raman amplifier and a rare earth doped fiber amplifier,
The Raman amplifier amplifies the wavelength-multiplexed signal light using a plurality of pump lights arranged at a frequency interval of (n + 0.5) times the Raman shift amount,
The rare earth-doped fiber amplifier is composed of a plurality of amplification units corresponding to the plurality of pump lights, and each amplification unit amplifies signal light in a corresponding wavelength band (n is an integer).
(Supplementary note 27) An optical transmission system in which wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is amplified by a Raman amplifier,
The Raman amplifier amplifies the wavelength-multiplexed signal light using pumping light arranged in a band of the wavelength-multiplexed signal light,
A monitoring signal for monitoring the state of the transmission system is arranged in the vicinity of the excitation light arranged in the band of the wavelength multiplexed signal light.
[0096]
【The invention's effect】
According to the present invention, a gain wavelength bandwidth wider than the Raman shift amount can be obtained using a Raman amplifier, and a large-capacity wavelength division multiplexing transmission system is realized. Moreover, since the auxiliary light for absorbing the energy of the signal light is arranged on the longer wavelength side than the signal light, it is possible to avoid that a part of the signal light is amplified more than necessary. Furthermore, since the rare earth doped fiber amplifier is used corresponding to the arrangement of the pumping light of the Raman amplifier, the combined use of the Raman amplifier and the rare earth doped fiber amplifier becomes easy.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical transmission system provided with a Raman amplifier of the present invention.
FIG. 2 is a configuration diagram of a Raman amplifier according to the present embodiment.
FIG. 3 is a diagram illustrating an outline of a Raman amplifier according to the present embodiment.
FIG. 4 is a diagram for explaining the operation of the Raman amplifier of the present embodiment.
FIG. 5 is a diagram for explaining the concept of Raman amplification for obtaining a wider gain wavelength bandwidth;
6 is a diagram for explaining the operation of the Raman amplifier shown in FIG. 5;
FIG. 7 is a diagram illustrating a method for setting signal light and excitation light.
FIG. 8 is a diagram illustrating a method for arranging excitation light.
FIG. 9 is a diagram illustrating an example of a method for supplying excitation light to a transmission line.
FIG. 10 is a diagram illustrating another example of a method for supplying excitation light to a transmission line.
11 is a modification of the method shown in FIG.
FIG. 12 is a diagram illustrating a function of adjusting a gain in a Raman amplifier.
FIG. 13 is a diagram illustrating a method for adjusting the optical S / N ratio of signal light.
FIG. 14 is a configuration diagram (No. 1) of an optical transmission system provided with a mixed transmission line fiber;
15 is a configuration diagram of a Raman amplifier in the system shown in FIG.
FIG. 16 is a configuration diagram (No. 2) of an optical transmission system provided with a mixed transmission line fiber;
17 is a configuration diagram of a Raman amplifier in the system shown in FIG.
FIG. 18 is a diagram for explaining the arrangement of auxiliary light (part 1);
FIG. 19 is a diagram (part 2) illustrating the arrangement of auxiliary light;
FIG. 20 is a diagram (No. 1) illustrating a method of supplying auxiliary light;
FIG. 21 is a diagram (No. 2) illustrating a method for supplying auxiliary light;
FIG. 22 is a diagram (No. 3) illustrating a method of supplying auxiliary light;
FIG. 23 is a diagram (No. 4) illustrating a method of supplying auxiliary light;
FIG. 24 is a configuration diagram of an optical transmission system in which a Raman amplifier and a rare earth doped fiber amplifier are mixed.
FIG. 25 is a correspondence table for determining the arrangement of excitation light.
FIG. 26 is a diagram (part 1) illustrating an arrangement example of excitation light;
FIG. 27 is a diagram (part 2) illustrating an arrangement example of excitation light;
FIG. 28 is a diagram illustrating a method of arranging monitoring control light.
FIG. 29 is a configuration diagram of a general optical repeater transmission system.
FIG. 30 is a diagram illustrating the principle of Raman amplification.
FIG. 31 is a configuration diagram of a wavelength division multiplexing optical transmission system using Raman amplification.
FIG. 32 is a diagram illustrating an amplification operation of an existing Raman amplifier.
[Explanation of symbols]
10, 20 Terminal
11, 22 Optical transmitter
12, 21 Optical receiver
30 Raman amplifier
31, 42 Excitation light source
32, 33 multiplexer
34 Optical circulator
41 Signal light source
43 MUX
71 Auxiliary light source
81a-81n rare earth doped fiber amplifier

Claims (2)

An optical transmission system in which a wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is amplified by a Raman amplifier and a rare earth doped fiber amplifier,
The Raman amplifier amplifies the wavelength multiplexed signal light using a plurality of pump lights arranged at a frequency interval of 1 / n of the Raman shift amount, and the rare earth doped fiber amplifier corresponds to the plurality of pump lights. An optical transmission system that includes a plurality of amplification units that amplify signal light in a corresponding wavelength band. However, n is 3 . An optical transmission system in which a wavelength multiplexed signal light obtained by multiplexing a plurality of signal lights by wavelength multiplexing is amplified by a Raman amplifier and a rare earth doped fiber amplifier,
The Raman amplifier amplifies the wavelength-multiplexed signal light using a plurality of pump lights arranged at a frequency interval of (n + 0.5) / (Raman shift amount), and the rare earth-doped fiber amplifier An optical transmission system that includes a plurality of amplification units corresponding to excitation light, and each amplification unit amplifies signal light in a corresponding wavelength band. However, n is 2 or 3 .

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